Lab Quiz 2 Flashcards
Nutritive media
-ones in which the basic growth nutrients are supplied as peptones (proteins reduced to short AA chains) and meat extracts or yeast extracts
-ex. chocolate agar, blood agar, MacConkey agar medium, Trypticase soy agar
Enriched media
-general supportive medium to which additional growth supplements have been added, such as blood, serum products, eggs, and/or vitamins essential for fastidious organisms
-ex. blood agar, chocolate agar
Selective Media
-basic or enriched medium to which antibiotics, dyes, or growth-inhibiting chemicals such as salts or alcohol are added in order to select for the organism that are resistant to these factors
-ex. MacConkey agar medium, mannitol salt agar, Colistin naldixic acid agar
Differential Media
-nutritive or enriched medium to which additional substrates such as carbs have been added. A visible difference between colonies is displayed based on the organism’s metabolic capabilities.
-ex. blood agar, MacConkey agar medium
fastidious bacteria
very strict growth requirements
MaConkey agar (MAC)
- type: selective and differential media
- purpose: selection of gram negative bacilli and for the differentiation of those organisms on the basis of lactose fermentation. (lactose vs. non-lactose)
- components: lactose (caarbon source), neutral red as pH indicator, bile salts and crystal violet inhibit. gram positive organisms
-lactose fermenter-pink
-non-lactose fermenter-colorless - when an organism ferments lactose, the drop in pH causes colonies to take on the pink to red appearance
Colombia Colistin Naladixic Acid Agar (CNA)
- type: selective media
- purpose: isolation of gram positive cocci
- components: peptones, beef extract and corn starch for energy sources, yeast extract (vitamins). colistin and naladixic acid in the medium is inhibitory to most gram negative organisms, allowing the gram positive to grow 5% sheep blood, provides X factor (hemin), is added for the determination of hemolytic reactions
- Incubation: 5-10% CO2 for 18-24h at 33-37C
- Alternative: PEA can be substituted; phenylethyl alcohol agar-the alcohol dries up the gram neg, prevents swarming and inhibits DNA synthesis
Chocolate agar
- type: enriched media
- Purpose: basic nutrient agar capable o promioting growth of all but the most fastidious organisms
-for the cultivation of fastidious organisms, especially neisseria and haemophilus species - components: casein and meat peptones, phosphate buffer to maintain pH, cornstarch to neutralize toxic fatty acids, hemoglobin for hemin (X factor), V factor (NAD), vitamins, amino acids, dextrose
- incubation: 5-10% CO2 for 18-24 at 33-37C
Blood agar
- type: enriched media
- Purpose: to facilitate growth of more fastidious bacteria and to observe hemolytic reactions
- components: casein and soy peptones which aid in bacterial growth. sheep blood enriches the medium and allows hemolytic reactions to be observed
- incubations: 5-10% CO2 for 18-24H at 33-37C
Trypticase Soy Broth (TSA)
- type: general nutrient media
- purpose: supports the growth of a wide variety of organisms including the many fastidious species. designed for the cultivation, storage and transport of pure cultures
- components: soybean meal- provides nutrients and casein (protein)- provides nutrients, basal medium for blood agar
- incubation: 33-37C, non-CO2
What media does S. epidermis grow on?
TSA , MSA
Mannitol salt agar (MSA)
Selective and differential culture medium
Mannitol Salt Agar (MSA) is a selective and differential culture medium used primarily to isolate and identify Staphylococcus aureus from clinical specimens. It contains 1% mannitol, 7.5% sodium chloride, and agar as a solidifying agent. The high salt concentration inhibits the growth of most bacteria except for staphylococci, while the mannitol serves as a fermentable carbohydrate, allowing for differentiation based on mannitol fermentation, which produces acid and changes the color of the medium.
Streptococcus pyogenes
-Catalase (-)
-Beta-hemolytic
-Group A- sensitivity to Bacitracin
-translucent, gray
Streptococcus pneumoniae
-Catalase (-)
-Alpha-hemolytic (green)
-Sensitive to Optochin
-Large, mucoid
Streptococcus viridians
-Catalase (-)
- Alpha-hemolytic (green)
-dry, tiny
-Resistant to Optochin
Streptococcus agalactiae
-Catalase (-)
-Beta-hemolytic (clear)
-small, translucent
-Group B: Resistant to Bacitracin
Staphylococcus epidermidis
-Catalase (+)
-Coagulase (-)
-NO Yellow colonies on TSA
-does not ferment mannitol
-grows on MSA
-TSA: white, small growth
-CNA: white growth
-BAP: white, gamma-hemolytic
-cellulitis and sepsis
Micrococcus
-Catalase (+)
-Coagulase (-)
-Yellow colonies on TSA
-doesn’t ferment mannitol
-no growth on MSA
-gram(+)- usually tetrads
Staphylococcus aureus
-Catalase (+)
-Coagulase (+)
-Ferments mannitol- yellow colonies
-BAP: White, buttery, beta-hemolytic
-MAC: no growth
-alcohol: large- very sensitive
-chlorox: small- not very sensitive
-hydrogen peroxide: large- very sensitive
-5% Lysol: large- very sensitive
-10% Lysol: medium- moderately sensitive
-mouthwash: none- resistant
-Quadricide: medium- moderately sensitive
-Wescodyne: medium- moderately sensitive
describe the advantages of using liquid vs solid media
Liquid:
-homogeneous distribution
-easy manipulation
-high growth rate
Solid:
-isolation of pure cultures
-visualization of colony morphology
-Enumeration of microorganisms
Pseudomonas aeruginosa
-gram (-) bacilli
-Blood agar (BAP): large, silver, metallic, beta-hemolytic, grape-like ador
MAC: non-lactose fermenter (clear)
-glucose (-)- cloudy red
-lactose (-)- cloudy red
-indole (-)- no color change
-urea: (-) or weak (+)- yellow/orange or slight pink
-MAC: non lactose fermenter- same color as media
-EMB: non lactose fermenter- same color as media
-CNA- no growth
-alcohol: small
-chlorox: none
-hydrogen peroxide: large
-5% Lysol: small
-10% Lysol: none
-mouthwash: none
-quadricide: small
-wescodyne: small
-food poisoning and cellulitis
Escherichia coli
-Gram (-) bacilli
-white/tan growth
-CNA: no growth
-BAP: white-gray, beta-hemolyic
-glucose (+)- cloudy yellow
-lactose (+)- cloudy yellow
-indole (+)- red/pink
-urea (-)- growth-slant yellow/orange
-MAC: lactose fermenter- dark pink centers
-EMB: lactose fermenter- purple centers
-CNA: no growth
-blood agar: white-gray, beta-hemolytic
-alcohol: medium
-chlorox: small
-hydrogen peroxide: large
-5% Lysol: medium
-10% Lysol: none
-quadricide: small
-wescodyne: small
Enterococcus faecalis
-Catalase (-)
-Esculin hydrolysis (breaks downs Esculin)
-gamma-hemolytic
-Grows on Bile Esculin
-alcohol: small
-chlorox: small
-hydrogen peroxide: large
-5% Lysol: medium
-10% Lysol: medium
-mouthwash: none
-quadricide: small
-wescodyne: medium
Proteus Mirabillis
-non-lactose fermenter- cloudy red
-urea (+)- growth slant pink/bright pink
-indole (-)- no color change
-glucose (+)- cloudy yellow
-MAC- non-lactose fermenter- same color as media
-EMB- non-lactose fermenter-same color as media
-CNA- no growth
-blood agar: gamma-hemolytic, gray, burnt-like appearance, wave-like growth
Bacillus subtilis resistances
-alcohol: small
-chlorox: small
-hydrogen peroxide: medium
-5% Lysol: medium
-10% Lysol: large
-mouthwash: none
-quadricide: medium
-wescodyne: medium
What is coagulase?
Enzyme that converts fibrinogen to fibrin
What is the reagent used to perform the coagulase test?
Rabbit plasma
How does coagulase relate to the organism’s ability to cause disease in healthy host?
Coloration between coagulation production. And exotoxins production of S. aureus
Clots form protecting bacteria-protect from phagocytosis
What is the significance of isolating Microccous from skin culture?
Part of normal flora
Why is mannitol salt agar considered selective?
High [salt] ➖ growth of most bacteria
Why is mannitol salt agar considered to be differential?
Differentiates between bacteria that can ferment mannitol (yellow) and those that cannot (clear)
What circumstances would lead you to choose blood agar to grow organisms?
Study hemolysis and grow fastidious organisms
What is added to blood agar to make it enriched?
5% sheep blood and growth factors
What circumstances would lead you to choose colistin naldixic acid agar?
Select for gram (+) bacteria in mixed culture
What is in MacConkey agar that makes it selective?
What makes it differential?
Crystal violet and bile salts
Lactose
When would you use MacConkey agar?
Select for gram (-) bacteria in a mixed culture
Why is NacCl added to TSA?
Maintain isotonic conditions
